Subject: RE: [mobile-ip] Mobile IPv6 - Issue 72 (Forwarding from previous CoA)

From: [email-masked]
Date: Mon, 16 Sep 2002 11:09:36 -0700

James,

in section 8.3 of MIPv6 spec we have a list of shoulds against  "all IPv6 routers". Further we say in section 10.2

      " If the node is not a router that implements home agent
       functionality, then the node MUST reject the Binding Update
       and MUST return a Binding Acknowledgement to the mobile node,
       in which the Status field is set to 132 (home registration not
       supported). "

So there are already recommendations for all routers. 

There seems to be a number of ways to interpret the text. Mine is that that BUs are sent to CNs and Home Agents, not to (access)routers. I agree that this mentioned in the context of handovers but so are all the other BUs, even the BU to set up the primary care-of address registration to the Home Agent. At least I fail to see the difference.

Obviously, I haven't been able to express/convince that this feature is a home agent feature at the visited link router. If the feature is turned of then you happen to have a Home Agent at your visited link. However, the functionality requires that the home agent feature is enabled there (in the access router), and the home agent support is advertised through Router Advertisements. Or alternatively, the MN may try to discover the home agent. This would not work with any other access router rather the one with the home agent feature on.  

Regards Hannu

-----Original Message-----
From: ext James Kempf [mailto:[email-masked]]
Sent: 16 September, 2002 9:55 AM
To: Flinck Hannu (NRC/MTView); Patil Basavaraj (NET/Dallas);
[email-masked]
Subject: Re: [mobile-ip] Mobile IPv6 - Issue 72 (Forwarding from
previous CoA)

Hannu

>
> Currently as the base specification describes the functionality it is
implemented with Home Agent functionality. There is nothing in addition to the
"normal" Home Agent behavior. This feature doesn't set any additional
requirements on access router nor home agent. If an access router has home agent
support enabled and the SA in place you have the feature. There is nothing to be
defined. The SA is the very same SA as with the Home Agent, provided that it can
be shared among a number of home agents.  We don't need to describe hoe this SA
is set in place, as we don't define how we set the SA for the home agent, do we.

The document refers to this functionality in the context of access routers, not
home agents. For example,
see Section 7.2:

  -  To allow a mobile node to send a Binding Update to a router on
       the link on which its previous care-of address is located, for
       purposes of establishing forwarding from this previous care-of
       address to its new care-of address (Section 11.6.6).

There are other such references throughout the document.

This confusion (is it an access router functionality or a home agent
functionality?) is part of the reason why I think it should be moved into the
fast handover document.

From my reading of the rest of the spec, with the exception of FoPCoA, there are
no requirements put on the access router whatsoever, so a standard IPv6 router
could be used. I believe this was one of the original design goals of MIPv6, for
example, see Section 2:

    -  There is no longer any need to deploy special routers as
       "foreign agents" as are used in Mobile IPv4.  In Mobile IPv6,
       mobile nodes make use of IPv6 features, to operate in any
       location without any special support required from the local
       router.

This feature compromises this basic design goal, and I believe it should be
moved to the fast handover spec, which explicitly requires changes in the access
router. Another possibility is that this design goal could be removed from the
MIPv6 spec, but I think that would be a mistake, since the rest of the spec
conforms with the design goal. Or the MIP group could make a recommendation that
all IPv6 routers be required to implement this functionality, and take the issue
to the IPv6 Working Group. Of these three, I think the easiest is to move it
into a spec that discusses MIPv6 handover directly and talks about specialized
MIPv6 access router functionality.

            jak

---

From: "James Kempf" <[email-masked]>
Date: Mon, 16 Sep 2002 12:30:43 -0700

Hannu,

,
> So there are already recommendations for all routers.

This only applies if the FoPCoA functionality is included in the specification.
If it is removed, there is no reason for a standard  IPv6 router to ever
interpret Binding Update. This text would need to be removed if FoPCoA is.

> There seems to be a number of ways to interpret the text. Mine is that that
BUs are sent to CNs and Home Agents, not to (access)routers. I agree that this
mentioned in the context of handovers but so are all the other BUs, even the BU
to set up the primary care-of address registration to the Home Agent. At least I
fail to see the difference.

FoPCoA requires a BU to be sent to the AR. If the AR implements HA
functionality, then it will do FoPCoA. If not, then it will do as the text
you've cited above. The difference is that IPv6 routers do not typically
implement HA functionality. Thus, this would be requiring additional
functionality of all IPv6 routers.

> Obviously, I haven't been able to express/convince that this feature is a home
agent feature at the visited link router. If the feature is turned of then you
happen to have a Home Agent at your visited link. However, the functionality
requires that the home agent feature is enabled there (in the access router),
and the home agent support is advertised through Router Advertisements. Or
alternatively, the MN may try to discover the home agent. This would not work
with any other access router rather the one with the home agent feature on.

I think the base spec should work with any IPv6 router. As far as I know, base
IPv6 routers don't require HA functionality. Anything else should be put into
separate document. The fast handover spec needs to have some text in it about
how an MN determines whether an AR can do fast handover, of course.

The MIPv6 needed to get finished yesterday. I don't think we need to delay more
until all the various little details of what it means to have an AR supply
"on-link" HA functionality to a random MN are worked out.

                jak